The Alliance for Paired Donation (APD) makes possible the transplantation of kidneys from living donors who otherwise are not transplanted because of ABO blood group incompatibility and/or the presence of donor-specific antibodies (Abs; DSA) in sensitized patients. The APD program may facilitate selection of donors and recipients for 2000 patients. Living donation accounts for 45-50% (~6000/year) of all kidney transplants performed in the United States. For Ohio alone, out of 3,300 patients each year diagnosed with end-stage renal disease, 825 patients would have a willing living donor. Since one third of these willing donors are typically incompatible, 275 patients have willing but incompatible donors. Similar nationwide analysis would account each year for 2000 willing but incompatible pairs. The APD program, composed of 75 transplant programs in 27 states, has already performed ~50 transplants, including 10 transplants in the first extended altruistic donor chain that included one altruistic donor. The proposed project needs to address important issues: 1) to develop and validate diagnostic tools to perform crossmatches of recipients and donors who are in different locations; 2) to improve the computer program for the analysis of crossmatch results and other parameters; and 3) to efficiently validate the survival results. At the present time, two used crossmatch assays (flow crossmatch and complement-dependent cytotoxicity) require live donor cells. Instead, we need to adapt an assay allowing using donor lymphocyte extracts wherein donor HLA antigens are captured onto beads (Bead-HLA assay). The second assay uses beads pre-coated with donor-type proteins to detect single HLA reactive anybodies (Single-HLA assay). Both these assays will be validated against the flow crossmatch method. The project has three aims: Aim 1: To establish sensitive and reproducible screening methods. In the first phase, all 4 assays (two old and two new) will be run with sera from sensitized patients against 20-30 different donors (1800 combinations). Aim 2: To improve matching by APD computer program. The findings from Aim 1 will be incorporated into the software by calculating the area under the curve (AUC) for the specificity and selectivity values using the Simpson's rule numerical integration methods. Aim 3: To validate the survival results made by APD program. The survival results will be followed after transplantation to validate the quality of choices and to further improve the APD program. At the grant conclusion, we will establish a centralized screening center able to enlist up to 2000 new pairs per year. As each transplant saves $200,000 during 5 years as compared with dialysis - to say nothing of the improved life of the patient - this proposal is cost-effective.